Scientific American recently had a piece that suggests this planet, Theia, formed in the inner solar system. The reasoning behind this being that the composition of the Moon and Earth are more similar than might be expected. Hence the idea that the two planets formed close to one another resulting in more rather than less similar composition with regard to heavy elements and so on.
Perhaps as interesting is this:
It is possible that the large low-shear-velocity provinces detected deep in Earth’s mantle may be fragments of Theia.[27][28] In 2023, computer simulations reinforced that hypothesis.[29][4]
Large low-shear-velocity provinces (LLSVPs), also called large low-velocity provinces (LLVPs) or superplumes, are characteristic structures of parts of the lowermost mantle, the region surrounding the outer core deep inside the Earth.[2]These provinces are characterized by slow shear wavevelocities and were discovered by seismic tomography of deep Earth. There are two main provinces: the African LLSVP and the Pacific LLSVP, both extending laterally for thousands of kilometers and possibly up to 1,000 kilometers (620 miles) vertically from the core–mantle boundary. These have been named Tuzo and Jason, respectively, after Tuzo Wilson and W. Jason Morgan, two geologists acclaimed in the field of plate tectonics.[3] The Pacific LLSVP (Jason) is 3,000 kilometers (1,900 miles) across and underlies four hotspotson Earth’s crust that suggest multiple mantle plumesunderneath.[4] These zones represent around 8% of the volume of the mantle, or 6% of the entire Earth.[1]
There’s a neat animation on the above wiki page that shows how large these LLSVP’s are, enormous structures really, as wide as continents and with massively greater volume/depth. It’s all too easy to believe that these are the remaining fragments of Theia. Worth noting that the ‘leading hypothesis’ as to their formation is somewhat less exciting.
The current leading hypothesis for the LLSVPs is the accumulation of subducted oceanic slabs. This corresponds to the locations of known slab graveyards surrounding the Pacific LLSVP. These graveyards are thought to be the reason for the high velocity zone anomalies surrounding the Pacific LLSVP and are thought to have formed by subduction zones that were around long before the dispersion—some 750 million years ago—of the supercontinent Rodinia. Aided by the phase transformation, the temperature would partially melt the slabs to form a dense melt that pools and forms the ultra-low velocity zone structures at the bottom of the core-mantle boundary closer to the LLSVP than the slab graveyards. The rest of the material is then carried upwards via chemical-induced buoyancy and contributes to the high levels of basalt found at the mid-ocean ridge. The resulting motion forms small clusters of small plumes right above the core-mantle boundary that combine to form larger plumes and then contribute to superplumes. The Pacific and African LLSVP, in this scenario, are originally created by a discharge of heat from the core (4000 K) to the much colder mantle (2000 K); the recycled lithosphere is fuel that helps drive the superplume convection. Since it would be difficult for the Earth’s core to maintain this high heat by itself, it gives support for the existence of radiogenic nuclides in the core, as well as implying that if fertile subducted lithosphere ceases to subduct in locations preferable for superplume consumption, it will mark the demise of that superplume.[4]
Either way, yet further evidence of how energetic (on long timespans) Earth and the Solar System more broadly are.
But there’s more, because some scientists have proposed that the very fact Earth has a Moon has contributed to life on this planet. Scientific American had this piece in 2009 that noted that oceanic tidal flow exacerbated climate changes resulting in ice ages and then periods of warming and with resultant movement of both animals and plant species accelerated certain evolutionary aspects.
Even more intriguing:
But is the influence of the lunar tides actually responsible for life itself?
If life originated around deep ocean hydrothermal vents (so-called black smokers), then the lunar tides played a minor role, if any, says James Cowen, a biogeochemical oceanographer at the University of Hawaii at Manoa. If, however, life originated in tidal waters, he says, then tidal cycles could have played a major role.
Simply put fast and frequent tides due to a shorter length of day could have provided just the right environment for life to spring into being. And all this because a Mars sized planet and the proto-Earth collided?
The Cedar Lounge Revolution 